fix(core): validate Plan.Root output name count

core/src/main/java/io/substrait/plan/Plan.java

@@ -3,9 +3,12 @@
 import io.substrait.SubstraitVersion;
 import io.substrait.extension.AdvancedExtension;
 import io.substrait.relation.Rel;
+import io.substrait.type.NamedFieldCountingTypeVisitor;
 import java.util.List;
 import java.util.Optional;
 import org.immutables.value.Value;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /** A complete Substrait plan: a set of root relations together with version and metadata. */
 @Value.Immutable
@@ -153,6 +156,8 @@ private static Version loadVersion() {
   /** A root relation of a plan together with the output field names it exposes. */
   @Value.Immutable
   public abstract static class Root {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Root.class);
+
     /**
      * Returns the relation producing this root's output.
      *
@@ -167,6 +172,26 @@ public abstract static class Root {
      */
     public abstract List<String> getNames();
 
+    /** Validates that the root output names match the input record type. */
+    @Value.Check
+    protected void check() {
+      final int actualNameCount = getNames().size();
+      if (actualNameCount == 0) {
+        LOGGER.warn(
+            "Plan.Root built without output names; this will be an error in the next release");
+        return;
+      }
+
+      final int expectedFieldCount =
+          NamedFieldCountingTypeVisitor.countNames(getInput().getRecordType());
+      if (actualNameCount != expectedFieldCount) {
+        throw new IllegalArgumentException(
+            String.format(
+                "Plan.Root names count (%d) must match input record type depth-first named-field count (%d)",
+                actualNameCount, expectedFieldCount));
+      }
+    }
+
     /**
      * Creates a builder for {@link Root}.
      *

core/src/main/java/io/substrait/relation/VirtualTableScan.java

@@ -1,8 +1,8 @@
 package io.substrait.relation;
 
 import io.substrait.expression.Expression;
+import io.substrait.type.NamedFieldCountingTypeVisitor;
 import io.substrait.type.Type;
-import io.substrait.type.TypeVisitor;
 import io.substrait.util.VisitationContext;
 import java.util.List;
 import java.util.Objects;
@@ -101,147 +101,4 @@ public <O, C extends VisitationContext, E extends Exception> O accept(
   public static ImmutableVirtualTableScan.Builder builder() {
     return ImmutableVirtualTableScan.builder();
   }
-
-  private static class NamedFieldCountingTypeVisitor
-      implements TypeVisitor<Integer, RuntimeException> {
-
-    private static final NamedFieldCountingTypeVisitor VISITOR =
-        new NamedFieldCountingTypeVisitor();
-
-    private static Integer countNames(Type type) {
-      return type.accept(VISITOR);
-    }
-
-    @Override
-    public Integer visit(Type.Bool type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.I8 type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.I16 type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.I32 type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.I64 type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.FP32 type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.FP64 type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.Str type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.Binary type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.Date type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.PrecisionTimestamp type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.PrecisionTime type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.PrecisionTimestampTZ type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.IntervalYear type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.IntervalDay type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.IntervalCompound type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.UUID type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.FixedChar type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.VarChar type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.FixedBinary type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.Decimal type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.Struct type) throws RuntimeException {
-      // Only struct fields have names - the top level column names are also
-      // captured by this since the whole schema is wrapped in a Struct type
-      return type.fields().stream().mapToInt(field -> 1 + field.accept(this)).sum();
-    }
-
-    @Override
-    public Integer visit(Type.ListType type) throws RuntimeException {
-      return type.elementType().accept(this);
-    }
-
-    @Override
-    public Integer visit(Type.Map type) throws RuntimeException {
-      return type.key().accept(this) + type.value().accept(this);
-    }
-
-    @Override
-    public Integer visit(Type.UserDefined type) throws RuntimeException {
-      return 0;
-    }
-
-    @Override
-    public Integer visit(Type.Func type) throws RuntimeException {
-      return 0;
-    }
-  }
 }

core/src/main/java/io/substrait/type/NamedFieldCountingTypeVisitor.java

@@ -0,0 +1,177 @@
+package io.substrait.type;
+
+/**
+ * Counts the number of field names required for a {@link Type} using Substrait's depth-first naming
+ * rules.
+ *
+ * <p>This is the same counting scheme used by {@link NamedStruct#names()}: top-level struct fields
+ * contribute one name each, and nested struct fields inside structs, lists, and maps also
+ * contribute names in depth-first order. Scalar types and other non-structural types do not
+ * contribute additional names.
+ *
+ * <p>Examples:
+ *
+ * <ul>
+ *   <li>{@code struct<i64, i64>} requires 2 names
+ *   <li>{@code list<struct<i64, i64>>} requires 2 names
+ *   <li>{@code map<struct<i64, i64>, struct<i64, i64, i64>>} requires 5 names
+ * </ul>
+ *
+ * <p>This utility is used anywhere the library needs to validate or reason about name counts
+ * without carrying the names themselves, such as {@code Plan.Root} and {@code VirtualTableScan}
+ * validation.
+ */
+public final class NamedFieldCountingTypeVisitor implements TypeVisitor<Integer, RuntimeException> {
+
+  private static final NamedFieldCountingTypeVisitor VISITOR = new NamedFieldCountingTypeVisitor();
+
+  private NamedFieldCountingTypeVisitor() {}
+
+  /**
+   * Returns the number of names required to describe {@code type} in Substrait's depth-first naming
+   * order.
+   *
+   * <p>For a top-level struct, this includes both the top-level field names and any nested struct
+   * field names required by compound child types.
+   *
+   * @param type the type to inspect
+   * @return the number of required names
+   */
+  public static int countNames(Type type) {
+    return type.accept(VISITOR);
+  }
+
+  @Override
+  public Integer visit(Type.Bool type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.I8 type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.I16 type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.I32 type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.I64 type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.FP32 type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.FP64 type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.Str type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.Binary type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.Date type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.PrecisionTime type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.PrecisionTimestamp type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.PrecisionTimestampTZ type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.IntervalYear type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.IntervalDay type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.IntervalCompound type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.UUID type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.FixedChar type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.VarChar type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.FixedBinary type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.Decimal type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.Func type) {
+    return 0;
+  }
+
+  @Override
+  public Integer visit(Type.Struct type) {
+    // Each struct field contributes its own name, plus any nested names required by that field's
+    // type.
+    return type.fields().stream().mapToInt(field -> 1 + countNames(field)).sum();
+  }
+
+  @Override
+  public Integer visit(Type.ListType type) {
+    // Lists do not add a name themselves, but list elements may contain nested structs.
+    return countNames(type.elementType());
+  }
+
+  @Override
+  public Integer visit(Type.Map type) {
+    // Maps do not add names themselves; any required names come from struct keys and/or values.
+    return countNames(type.key()) + countNames(type.value());
+  }
+
+  @Override
+  public Integer visit(Type.UserDefined type) {
+    return 0;
+  }
+}